Manufacturing process for liquid crystalline polymer

ABSTRACT

The properties of a liquid crystalline polymer (LCP) containing ester linkages and made in the presence of an excess of diol are improved by treating the LCP with a dicarboxylic acid at elevated temperature. The resulting LCPs are useful as molding resins and for films.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/537,539, filed Jan. 20, 2004 and U.S. Provisional Application No.60/500,087, filed Sep. 4, 2003.

FIELD OF THE INVENTION

The present invention is directed to processes for producing liquidcrystalline polymers. The processes provide liquid crystalline polymershaving improved properties. The processes include reacting dicarboxylicacids with aliphatic esters of diols and optionally hydroxycarboxylicacids, wherein an excess of diol (ester) is present, and treating theresulting LCP with a dicarboxylic acid.

BACKGROUND

Liquid crystalline polymers (LCPs) are items of commerce, thousands oftons being made annually. They are used in a myriad of ways, as moldingresins and in films, for example to make electrical and electronicparts, automotive parts, and medical parts. LCPs are most often providedas polyesters, but also available as poly(ester-amides). Thecondensation reaction to form the polyester linkages is most commonlydone by condensing at elevated temperatures one or more dicarboxylicacids with the aliphatic esters of one or more diols and/or thealiphatic monoesters of one or more hydroxycarboxylic acids. Althoughthe aliphatic esters can be “preformed”, that is, the ingredients addedto the polymerization process as aliphatic esters, for economic reasonsthe aliphatic esters are usually made in situ by adding an appropriateamount of an aliphatic carboxylic anhydride to the polymerizationmixture to form the aliphatic ester(s).

Typically all of the monomers needed to form the LCP are added to areactor together with an amount of aliphatic carboxylic anhydride,usually acetic anhydride, to form ester groups with all of the hydroxylgroups of the diols and hydroxycarboxylic acids monomer present in theester groups. The mixture is heated to complete ester formation and thecarboxylic acid formed is removed by distillation. Heating is continued,with concomitant distillation of carboxylic acid, to perform thecondensation polymerization, and finally usually vacuum is applied tocomplete the polymerization. Alternately melt polymerization can bediscontinued at some point and the (pre)polymer further polymerized tothe desired molecular weight using so-called solid state polymerization.It may be desirable, particularly when one of the diols used is somewhatvolatile, to use an excess of the diol in the polymerization, to make upfor any possible losses of the diol (or its diester) by inadvertentvolatilization and removal from the polymerization. However, the LCPsobtained may not have optimal properties for desired uses, and inparticular can be more brittle than desired for some applications.

U.S. Pat. No. 6,294,618 describes the treatment of LCPs with variousfunctional compounds to reduce the viscosity of the LCPs.

LCPs having improved properties, such as tensile or flexural elongation,are desirable.

SUMMARY OF THE INVENTION

The present invention is directed to processes for making liquidcrystalline polymers (LCPs). There is no mention of LCPs made with anexcess of diol present, nor of an

One aspect of the present invention is, a process comprising:

-   -   (a) forming a liquid crystalline polymer from ingredients        comprising one or more first dicarboxylic acids, aliphatic        diesters of one or more first diols and optionally aliphatic        esters of one or more hydroxycarboxylic acids; and    -   (b) contacting the liquid crystalline polymer with about 2 to        about 200 milliequivalents per kg of said liquid crystalline        polymer of a second dicarboxylic acid, at a temperature        sufficient to cause reaction of the second dicarboxylic acid        with the liquid crystalline polymer for a period of time        sufficient to cause at least about a 10% increase in the tensile        elongation of the liquid crystalline polymer;

provided that the molar ratio of the total of first diols present to thetotal of first dicarboxylic acids is 1.01 or more.

DETAILED DESCRIPTION

Herein certain terms are used, and they are described below.

By a liquid crystalline polymer is meant that the polymer is anisotropicin the TOT, or any similar test method, as described in U.S. Pat. No.4,075,262, which is hereby incorporated herein by reference. Preferredpolymers are liquid crystalline polyesters, and it is further preferredthat the liquid crystalline polyesters be aromatic polyesters. Byaromatic polyesters is meant that the carbon and oxygen atoms at theends of the group —C(O)O— of the ester linkages are each bonded tocarbon atoms that are part of aromatic rings.

By a diol is meant an organic compound having two hydroxyl groups, andpreferably no other functional groups that can form ester linkages.Preferred diols are aromatic diols, in which both hydroxyl groups arebound to carbon atoms of one or two different aromatic rings.

By a dicarboxylic acid is meant an organic compound having two carboxylgroups, and preferably no other functional that can form ester linkages.Preferred carboxylic acids are aromatic dicarboxylic acids, in whichboth carboxyl groups are bound to carbon atoms of one or two differentaromatic rings.

By a hydroxycarboxylic acid is meant an organic compound having onehydroxyl group and one carboxyl group, and preferably no otherfunctional groups which can form ester linkages. Preferrredhydroxycarboxylic acids are aromatic hydroxycarboxylic acids, in whichthe hydroxyl and carboxyl groups are bound to carbon atoms of one or twodifferent aromatic rings.

By an aliphatic diester of a diol is meant a diester formed from thediol and 2 carboxyl groups (R¹CO₂—, wherein R¹ is alkyl or substitutedalkyl) derived from aliphatic carboxylic acids. By an aliphatic ester ofa hydroxycarboxylic acid is a meant a monoester formed from thehydroxycarboxylic acid and one carboxyl group derived from an aliphaticcarboxylic acid. Preferably some or all of such esters are acetates.

By “tensile elongation” is meant the elongation to break when measuredby ASTM Method D638 using an extension rate of 5.1 mm/min (0.2 in/min),and a Type I bar. Measurements are made using strain gauges toaccurately measure the usually small strain to break.

Useful dicarboxylic acids for treating the LCP include terephthalicacid, 2,6-napthalenedicarboxylic acid, isophthalic acid, 4,4′-bibenzoicacid, 2-methylterephthalic acid, and adipic acid. Preferred dicarboxylicacids are isophthalic acid, 2,6-naphthalene dicarboxylic acid, andterephthalic acid, and terephthalic acid and 2,6-naphthalenedicarboxylic acid are especially preferred. Other preferred seconddicarboxylic acids are aromatic dicarboxylic acids, in which bothcarboxyl groups are bound directly to an aromatic ring carbon atom.

Useful dicarboxylic acids as monomers for the LCP include terephthalicacid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-bibenzoicacid, and 1,8-naphthalenedicarboxylic acid. Useful diols as monomers forthe LCP include ethylene glycol, hydroquinone, resorcinol,4,4′-biphenol, 2,6-dihydroxynaphthalene, 1,8-dihydroxynaphthalene,bisphenol-A, and bisphenol-S. Hydroquinone and 4,4′-biphenol arepreferred diols, and hydroquinone is especially preferred. Usefulhydroxycarboxylic acids as monomers for the LCP include 4-hydroxybenzoicacid, 6-hydroxy-2-napthoic acid, and t-butyl-4-hydroxybenzoic acid.Preferred hydroxycarboxylic acids are 4-hydroxybenzoic acid and6-hydroxy-2-napthoic acid, and 4-hydroxybenzoic acid is especiallypreferred.

When the LCP is made, the molar ratio of total diols to totaldicarboxylic acids 1.01 or more (the diols are present in at least 1%molar excess), preferably 1.02 or more and especially preferably 1.03 ormore. Preferably the molar ratio of total diols to total dicarboxylicacids is about 1.5 or less, more preferably about 1.10 or less. Anylower limit and any upper limit of diols can be combined to form apreferred range.

In one preferred method of preparing the LCP, the LCP is preparedcompletely in the melt, and then treated with the dicarboxylic acid. Inanother preferred method, the LCP is prepared initially in the melt andthen the molecular weight of the LCP is raised in a solid statepolymerization. After the solid state polymerization the LCP is treatedwith the dicarboxylic acid.

The treatment of the LCP with the dicarboxylic acid is most effectivelycarried out when the LCP is in the melt. In one preferred method the LCPis melted and mixed with the dicarboxylic acid in a melt mixer used forpolymers such as a single or twin screw extruder, or kneader. Themixture is heated to a temperature above the melting point of the LCP atwhich the elongation of the LCP is increased by a desired amount in thetime the mixture is being heated and mixed in the mixer. While it is notintended that the present invention be bound by any particular theory ormechanism, it is believed that the elongation of the LCP is increasedwhen the dicarboxylic acid reaches a temperature at which it can reactwith other species present in the melt. The LCP and dicarboxylic acidcan be premixed as solids before being put into the mixer, or can beadded separately and mixed in the mixer.

Other materials such as fillers, reinforcing agents, lubricants,pigments, and other materials known for use in making LCPs can be mixedinto the LCP at the same time as the dicarboxylic acid. In testmeasurements, the elongation of the LCP (including the other ingredientsmixed into the LCP) is compared to that of an LCP having the samecomposition and made in the same way, but without the dicarboxylic beingpresent. Alternatively, a composition containing the LCP and otheringredients can be prepared first and then treated with the dicarboxylicacid. The elongation of the resulting LCP is compared to that of thesame composition treated in the same way but without dicarboxylic acidbeing added. “Pure” LCP can be treated with dicarboxylic acid and theelongation thereof compared to that of “pure” LCP treated in the samemanner but without dicarboxylic acid.

Examples of useful other ingredients include glass fiber, milled glassfiber, hollow or solid glass spheres, mica, talc, titanium dioxide,carbon black, carbon fiber, and aramid fiber, and lubricants such aspolyethylene waxes.

The amount of (second) dicarboxylic acid used is at least about 2, andpreferably at least about 5 (meq)/kg LCP (based on only the LCP) Theamount of (second) dicarboxylic acid added in the treatment of the LCPis about 200 or less, preferably about 100 or less, and more preferablyabout 50 or less (meq)/kg LCP (LCP only in the composition).“Equivalents” means equivalents of carboxylic acid functionality, andone millimole of dicarboxylic acid contains two meq of carboxyl groups.Any lower limit and any upper limit of dicarboxylic acid contents can becombined to form a preferred range.

Other types of difunctional compounds can be used in addition to thedicarboxylic acid used for the treatment of the LCP. Functionalities insuch compounds can include hydroxy, carboxylate, ester, and primary orsecondary amine, and hydroxy is preferred. Useful hydroxy compoundsinclude diols and water (by definition herein a difunctional compound),and of the diols aromatic diols are especially preferred. Usefularomatic diols include hydroquinone, resorcinol, 4,4′-biphenol,2,6-dihydroxynaphthalene, 1,8-dihydroxynaphthalene, bisphenol-A, andbisphenol-S. Such preferred aromatic diols are hydroquinone and4,4′-biphenol, and 4,4′-biphenol is especially preferred.

Water is also an especially preferred hydroxy compound, and can be usedalone or in combination with a diol, especially an aromatic diol. Thewater can be added to the process as water, or in a form that underprocess conditions generates water. For example, the water can be addedas a hydrate or other compound that under the process (temperature)conditions “loses” water. Such hydrates and other compounds includealuminum oxide trihydrate, copper sulfate pentahydrate, barium chloridedihydrate, and calcium sulfate dihydrate.

Preferably the total molar amount of other difunctional compound(s) (notincluding water, if present) does not exceed twice the total molaramount of the dicarboxylic acid added to treat the LCP, and is morepreferably about 20 to about 100 percent (by moles) of the amount ofsuch dicarboxylic acid added. If water is present, it can be added inmuch larger amounts compared to the total molar amount of the seconddicarboxylic acid added, independent of and not including any otherdifunctional compound added. If water is used, it is preferably used ina molar ratio of 0.2:1 to about 10:1 to the dicarboxylic acid added.That is, the amount of water is preferably from about 20 to about 1000mole percent based on the number of moles of the second dicarboxylicacid. The amount of water in a hydrate is taken only as the amount thatis “freed” i.e., released, under the process conditions. For example, atrihydrate may yield only two moles of water per mole of trihydrateunder certain temperature conditions. Larger amounts of water may beneeded because not all the water added may be effective in the process.If added as water, rather than generated in situ, much if not most ofthe water may be lost because it may vaporize and/or not be very solublein the process ingredients. The same may be true (possibly to a lesserextent) for water contained in hydrates. The amount of water (orhydrate, since water may be present as water of hydration) needed toachieve a certain viscosity reduction under a given set of processconditions can be determined by simple experimentation. It has beennoted that the amount of water (hydrate required is determined to someextent by the scale of the equipment used and/or the “tightness” (thepropensity to lose water vapor) of that equipment.

When present in moderate amounts, such as the amounts recitedhereinabove, other difunctional compounds, especially hydroxy compounds,are believed to lower the melt viscosity of the LCP without greatlyadversely affecting other physical properties of the LCP. Lower meltviscosity is advantageous in certain melt forming operations such asinjection molding, since it can allow for easier and/or more completemold filling, especially if the mold has narrow or thin openings orpassageways.

When the LCP is treated with the dicarboxylic acid, the tensileelongation of the LCP is preferably increased by at least about 10percent, more preferably by at least about 20 percent. The percentageelongation increase is calculated using the equation

$\% = \frac{\left( {{EAT} - {EBT}} \right) \times 100}{EBT}$wherein EAT is percent tensile elongation after treatment (with thedicarboxylic acid), and EBT is percent tensile elongation beforetreatment.

The LCP is useful as a molding resin, for example, for making shapedparts useful for electrical and electronic apparatuses, in automotivevehicles, in medical devices and in films for use in packaging. Shapedparts can be made by melt molding the LCP containing composition, forexample by injection molding, extrusion, blow molding, ram injectionmolding, rotational molding, and compression molding. Films may be madeextrusion through a straight die or through a rotating die.

EXAMPLES

In the following Examples the melt viscosities were determined using aKayness Model 8052 viscometer, Kayness Corp., Morgantown Pa., U.S.A., at350° C. (unless otherwise noted) and a shear rate of 1000/sec. Tensileproperties were determined by the method of ASTM D638, using the Type Itest sample shape, at a sample thickness of 0.32 cm (⅛″), and anelongation rate of 0.51 cm/min (0.2 inches/min). The tests were runusing strain gauges so that the usually small strains to break could bemeasured accurately.

In the Examples, except where noted, all parts are parts by weight.

In the Examples, the following materials are used:

ATH—alumina trihydrate

BP—4,4′-biphenol

GF—Vetrotex® 991 glass fiber, available from Saint-Gobain VetrotexAmerica, Valley Forge, Pa. 19482, USA.

LCP1—a liquid crystalline polymer made from hydroquinone/terephthalicacid/2,6-naphthalenedicarboxylic acid/4-hydroxybenzoic acid100/30/70/150 molar parts, wherein the initial ratio of hydroquinone todicarboxylic acids was 1.05, and acetic anhydride was added to thepolymerization to form aliphatic acetates in situ

LCP2—a liquid crystalline polymer as LCP1, but polymerized to a highermolecular weight prior to compounding

Lube—Licowax®V PE190 polyethylene wax, available from Clarient Corp.,Charlotte, N.C. 28205, USA.

NDA—2,6-naphthalene dicarboxylic acid

MV—melt viscosity, in Pa·s at 1000 sec⁻¹ shear rate

Ten. Elong.—tensile elongation to break, %

Ten. Mod.—tensile modulus, GPa

Ten. Str.—tensile strength, MPa

TiO₂—TiPure® R-100 titanium dioxide available from E.I. DuPont deNemours & Co., Inc., Wilmington, Del. 19898, USA.

TPA—terephthalic acid

Examples 1-11 and Comparative Example A-E

All of the compositions contained 2.0% TiO₂ (Example 11 had 4.0% TiO₂),0.2% Lube, 45.0% GF, the amounts (percent by weight based on the totalcomposition) of BP and TPA indicated in Table 1, and the remainder LCP1.The compositions were mixed on a 30 mm Werner and Pfleiderer twin screwextruder at a screw speed of 275 rpm. Barrel temperatures were 360, 370,370, 320, 300, 300, 320, 330° C. (barrels 2-8 and the die) for Examples1-7 and comparative Examples A and B, and 310° C. for barrels 2-8, (die330° C.) for Examples 8-11 and comparative Examples C-E. Thecompositions were pelletized upon exiting from the extruder. The pelletswere molded into test pieces on a 1.5 oz. Arberg injection moldingmachine. Barrel temperatures were 330° C. for Examples 1-7 andcomparative Examples A and B, and 320° C. for Examples 8-11 andcomparative Examples C-E. Mold temperatures were all 70° C. The meltviscosities of the compositions were determined, as were the tensileproperties, and the results reported in Table 1.

TABLE 1 Ten. Ten. Ten. Ex. TPA BP MV Mod. Str. Elong. A 0.0 0.0 36 15.3116 2.4 B 0.0 0.2 22 13.5 113 2.4 1 0.4  0.0. 28 11.0 108 3.7 2 0.6 0.019 11.4 107 3.7 3 0.5 0.1 21 12.0 107 3.5 4 0.4 0.2 22 12.7 107 3.5 50.1 0.1 20 12.6 123 3.4 6 0.2 0.2 20 13.1 112 3.5 7 0.3 0.3 17 12.5 1103.4 C  0.0. 0.0 41 13.0 114 3.1 D  0.0. 0.3 20 12.0 106 3.0 E 0.0 0.6 1113.0 102 2.6 8 0.8 0.0 19 10.3 113 3.9 9 0.4 0.2 25 11.2 115 3.6 10  0.40.4 14 10.8 118 4.0 11  0.4 0.4 15 12.0 115 4.1

Testing of flexural properties showed trends parallel to those obtainedin tensile testing. Despite having lower melt viscosities than thecorresponding compositions in which TPA nor BP were present, thecompositions containing TPA, whether BP was present or not, had a highertensile elongation to break than the compositions not containing TPA orcontaining only BP. This indicates that the compositions containing TPAwere tougher than the other compositions. In addition compositions thatcontained both TPA and BP were somewhat lighter (whiter) in color.

Examples 12-19 and Comparative Example F

All of the compositions contained 2.0 TiO₂, 0.2% Lube, 45.0% GF, theamounts of NDA, BP and ATH (in weight percent of the total composition)indicated in Table 2, and the remainder LCP2. The compositions weremixed on a 30 mm Werner and Pfleiderer twin screw extruder at a screwspeed of 225 rpm. Barrel temperatures were 360, 360, 360, 360, 360, 330,330, 330, 330° C. (barrels 2-9 and the die). The compositions werepelletized upon exiting from the extruder. The pellets were molded intotest pieces on a 1.5 oz. Arberg injection molding machine. Barreltemperatures were 330° C. and mold temperatures were all 70° C. The meltviscosities (measured at 340° C.) of the compositions were determined,as were the tensile properties, and the results reported in Table 2.

TABLE 2 Ten Ten Ten Ex. NDA BP ATH MV Mod Str Elong F 0.00 0.00 0.00 5415.3 125 3.2 12 0.06 0.00 0.00 58 16.2 136 4.1 13 0.06 0.06 0.00 47 15.0133 3.8 14 0.06 0.18 0.00 45 15.3 110 2.7 15 0.06 0.00 0.02 52 16.8 1313.7 16 0.06 0.00 0.06 40 16.5 136 4.0 17 0.06 0.00 0.08 41 16.1 134 3.918 0.06 0.06 0.03 38 16.7 132 3.5 19 0.06 0.06 0.06 37 16.5 136 3.8

What is claimed is:
 1. A process comprising: (a) forming a liquidcrystalline polymer from ingredients comprising one or more firstdicarboxylic acids, one or more first diols and optionally one or morehydroxycarboxylic acids; and (b) contacting said liquid crystallinepolymer with about 2 to about 200 milliequivalents per kg of said liquidcrystalline polymer of a first type of difunctional compound and with asecond type of difunctional compound, wherein the first type ofdifunctional compound is a second dicarboxylic acid and wherein thesecond type of difunctional compound is a second diol, at a temperaturesufficient to cause reaction of said second dicarboxylic acid and saidsecond diol with said liquid crystalline polymer for a period of timesufficient to cause at least about a 10% increase in the tensileelongation of said liquid crystalline polymer; provided that the molarratio of the total of first diols present to the total of firstdicarboxylic acids present in (a) is 1.01 or more.
 2. The process asrecited in claim 1 wherein said molar ratio is from about 1.03 to about1.5.
 3. The process as recited in claim 1 wherein from about 5 to about50 milliequivalents per kg, based on said liquid crystalline polymer, ofa second dicarboxylic acid are present.
 4. The process as recited inclaim 1 wherein said liquid crystalline polymer contains repeat unitsderived from one or more of terephthalic acid, isophthalic acid,2,6-naphthalenedicarboxylic acid, 4,4′-bibenzoic acid, and1,8-naphthalenedicarboxylic acid, ethylene glycol, hydroquinone,resorcinol, 4,4′-biphenol, 2,6-dihydroxynaphthalene,1,8-dihydroxynaphthalene, bisphenol-A, bisphenol-S, 4-hydroxybenzoicacid, 6-hydroxy-2-napthoic acid, and t-butyl-4-hydroxybenzoic acid. 5.The process as recited in claim 1 wherein said liquid crystallinepolymer contains repeat units derived from one or more of terephthalicacid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, hydroquinoneand 4,4′-biphenol, 4-hydroxybenzoic acid and 6-hydroxy-2-napthoic acid.6. The process as recited in claim 1 wherein said second dicarboxylicacid is an aromatic dicarboxylic acid.
 7. The process as recited inclaim 1 wherein said second dicarboxylic acid is one or more of2,6-naphthalenedicarboxylic acid, isophthalic acid, 4,4′-bibenzoic acid,2-methylterephthalic acid, and adipic acid.
 8. The process as recited inclaim 1 wherein said second dicarboxylic acid is one or both ofterephthalic acid and 2,6-naphthalene dicarboxylic acid.
 9. The processas recited in claim 1 wherein said tensile elongation is increased by atleast about 20 percent.
 10. The process as recited in claim 1 wherein athird type of difunctional compound is also present.
 11. The process asrecited in claim 1 wherein said second type of difunctional compound ispresent in an amount of about 20 to about 100 mole percent of saidsecond dicarboxylic acid.
 12. The process as recited in claim 10 whereinsaid third type of difunctional compound comprises water.
 13. Theprocess as recited in claim 12 wherein said water is present in the formof a hydrate.
 14. The process as recited in claim 13 wherein saidhydrate is alumina trihydrate.
 15. The process as recited in claim 12,wherein the amount of said water present is from about 20 to about 1000mole percent based on the number of moles second dicarboxylic acid. 16.A polymer made according to the process of claim
 1. 17. A shaped partformed from a polymer made according to the process of claim
 1. 18. Afilm formed from a polymer made according to the process of claim
 1. 19.The process as recited in claim 1, wherein the total molar amount of thesecond difunctional compound does not exceed twice the total amount ofthe second dicarboxylic acid.
 20. The process as recited in claim 1,wherein the step of forming the liquid crystalline polymer includesforming diesters from the one or more first diols and a carboxylic acid.21. The process as recited in claim 20, wherein the carboxylic acid isan aliphatic carboxylic acid and the diesters are aliphatic diesters.22. The process as recited in claim 1, wherein the step of forming theliquid crystalline polymer includes forming esters from the one or morehydroxycarboxylic acids and a carboxylic acid.
 23. The process asrecited in claim 22, wherein the carboxylic acid is an aliphaticcarboxylic acid and the esters are aliphatic esters.
 24. The process asrecited in claim 23 wherein said aliphatic esters are acetates.
 25. Theprocess as recited in claim 23 wherein said aliphatic esters are formedin situ.
 26. The process as recited in claim 1 wherein said molar ratiois from about 1.02 to about 1.10.
 27. The process as recited in claim 1,wherein the second diol is 4,4-biphenol.